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2003 Nissan Xterra catalytic converter confusion


I just bought a 2003 Nissan Xterra. It has the 3.3L engine and after taking it in to a shop, reading the Haynes manual, and searching on line I am even more confused. Before purchasing the car I looked it over, crawled under, flicked every possible switch, and even hooked up my pocket scan. So it goes without saying that after purchasing it, and driving it for two hours the check engine light came on. I scanned again and the codes came back for catalytic converter failure(s). I took it in to the shop to see what they thought. Of course they said I needed to replace the catalytic converters, but I haven’t heard back from them. I have no problem doing the work myself but I can’t find answers for my questions. From what I can see the catalytic converters are “one piece” with the exhaust manifolds, with O2 sensors before and after. The problem is that 18" after those are two more canisters. The mechanic that checked the car says those are the actual cotalytic converters, but even if I change the (catalytic converters I may need to change the pre-catalytic convers. When I look up catalytic converters in the online parts, every site shows both.

If anyone can answer the following it would be greatly appreciated.

How many catalytic converters are there on this car?
Which are pre-cats, which are actual converters?
Are there aftermarket/performance systems that would meet the OBD2 requirements? (Magnaflow/Pace Setter/etc.) *Based on the over the phone quote from dealership I could replace the complete system with a performance system, but I am affraid to chage one problem for another.

First off you have to determine that it actually IS a catalytic converter. The ECU determines the cat is bad by the readings it’s receiving from the O2 sensors. Many times the O2 sensors fail and give a false reading and the ECU things it’s the Cat that’s failed and throws the code.There are tests you need to preform to determine if it’s the Cat or the O2 Sensor. Just scanning it won’t give you the answer.

If it is the Cat…look at getting an aftermarket cat. Far cheaper then the dealer. As with any exhaust system…there are several possibilities. Doesn’t really matter as long as they were designed for that engine.

@Sahmwong did you buy the car from a dealer or used car lot?

If you did, you should go right back. I suspect they may have known about this issue and purposefully didn’t mention it.
The seller probably cleared codes right before you inspected and bought the car.
A dealer isn’t allowed to sell a car with the MIL on.
When you hooked up your code reader, the catalyst monitor hadn’t yet run to completion. So at that precise moment the code hadn’t “matured” yet. But on the drive home, the monitor completed, the code matured, and the MIL illuminated.
It sounds pretty shady to me, because you got the P0420 and P0430 codes and the MIL 2 hours after buying the car.
Those are your fault codes, right?
It’s possible that the real problem is the oxygen sensors, but that’s besides the point.

I think you got taken.

You need to go back, demand a refund of your money and/or demand that he fix it, at his cost.

First, thanks for your replies.
Mike, I will check out the O2 sensors before I buy new cats. I just got the specs so I can back probe them and know what I am looking at. That said, I also found out that this was a known problem (cats failing around100K mile) with the suv. My understanding was Nissan covered them for 8 years(which doesn’t help me). Anyways, oddly enough when I was checking the specs for the O2 sensors it says to heat them up to 600 degrees… which is what the mechanic said the problem was both O2 sensors being the same temp… And I thought Oxygen sensors monitored oxygen, not temperature…
unfortunatly I bought it from an auction, and only had engine/transmission warrenty. I knew the risk up front, and I took it. I could go on about the risks involved in everything, but in the end, it is what it is. I just have to man up and climb under. Good thing it has some ground clearance…

If you bought them from an auction, you’re likely SOL, but check your state’s laws dealing with reselling used cars anyway. State laws vary.

I’d bet that the CEL was reset. But probably not by the auction house. In NH it’s perfectly legal for even a dealer to sell a used car that will not pass inspection as long as they notify the buyer in writng that it’s being sold as-is in an uninspectable condition.

As to the 600F, the catalyst in the converter (the platinum-palladium) isn’t effective in causing the nitrogen and oxygen molecules to seperate and the carbon monoxide and the carbon to capture oxygen atoms and become carbon dioxide (known as the “second burn”) until it’s heated to 600F. In application the exhaust heats them up. Your cylinder temps can get above 2,000 degrees, and that’ll easily heat up the catalyst, especially since it’s coated onto ceramic, which is great at retaining heat. Cook a stew in a ceramic pot and it’ll take all evening to cool. It’ll keep the stew hot well after the meal is over. That’s why it has to be tested at 600F or above. That’s its normal operating environment.